It needs a verb to match its number (singular) in the subject, therefore, Ice-cream costs ten euros. If you were to use an article, "An ice-cream costs ten euros" it would be the same. If you were to say, "Those ice-creams cost ten euros", you are using it in its plural form and clearly referring to more than one.
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AnonymousCan I use both variants?No. Ice-cream is singular. Only costs is possible.